1. Field of the Invention
The present invention relates to a method and a device for high-resolution acousto-optic programmable filtering in the infrared region.
This method applies in particular to acousto-optic programmable filtering for the mid-infrared region ranging from a wavelength λ in vacuum of 5 to 20 μm.
2. Description of the Prior Art
The transparency window of TeO2, which extends from 0.35 to 4.5 μm, does not allow development of an Acousto-Optic Programmable Filter (AOPDF) for the mid-infrared region ranging from 5 to 20 μm, such as that described in the article published in the journal J.Phys.France 12 (2002) Pr. 69/75: “Theory and Performance of the Acousto-Optic Programmable Dispersive Filter used for Femtosecond Laser Pulse Shaping”.
Generally, it is known that the best materials for such an application are compounds of mercury such as Hg2Cl2, Hg2Br2 and Hg2I2. Amongst these materials, only calomel (Hg2Cl2) is today capable of industrial use.
In this wavelength range of 5 to 20 μm, calomel, which is a uniaxial birefringent crystal, is only slightly dispersive. Its ordinary index n0 is close to 1.898 and its extraordinary index ne on the axis [110] is close to 2.445. The propagation speed of transverse acoustic waves is very slow on the axis [110] (V110=347 m/s) and much faster on the axis [001] (V001=1084 m/s).